Settable compositions comprising cement kiln dust and rice husk ash and methods of use

ABSTRACT

Embodiments disclose method and compositions that comprise cement kiln dust and rice husk ash. An embodiment comprises a method of cementing comprising: placing a settable composition into a subterranean formation, the settable composition comprising cement kiln dust, rice husk ash, and water; and allowing the settable composition to set. Another embodiment discloses a settable composition comprising cement kiln dust, rice husk ash, and water.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.13/479,476, entitled “Settable Compositions Comprising Cement Kiln Dustand Rice Husk Ash and Methods of Use, filed May 24, 2012, issued as U.S.Pat. No. 8,327,939, which is a continuation-in-part of U.S. applicationSer. No. 12/975,196, entitled “Settable Compositions Comprising CementKiln Dust, Unexpanded Perlite, and/or Pumicite,” filed on Dec. 21, 2010,which is a continuation-in-part of U.S. patent application Ser. No.12/821,412, entitled “Methods of Plugging and Abandoning a Well UsingCompositions Comprising Cement Kiln Dust and Pumicite,” filed on Jun.23, 2010, issued as U.S. Pat. No. 8,307,899, which is acontinuation-in-part of U.S. patent application Ser. No. 12/606,381,issued as U.S. Pat. No. 7,743,828, entitled “Methods of CementingSubterranean Formation Formations Using Cement Kiln Dust in CompositionsHaving Reduced Portland Cement Content,” filed on Oct. 27, 2009, whichis a continuation-in-part of U.S. application Ser. No. 12/420,630,issued as U.S. Pat. No. 7,631,692, entitled “Settable CompositionsComprising a Natural Pozzolan and Associated Methods,” filed on Apr. 8,2009, which is a continuation-in-part of U.S. patent application Ser.No. 12/349,676, issued as U.S. Pat. No. 7,674,332, entitled “ExtendedSettable Compositions Comprising Cement Kiln Dust and AssociatedMethods,” filed on Jan. 7, 2009, which is a divisional of U.S. patentapplication Ser. No. 12/034,886, issued as U.S. Pat. No. 7,478,675,entitled “Extended Settable Compositions Comprising Cement Kiln Dust andAssociated Methods, filed on Feb. 21, 2008, which is acontinuation-in-part of U.S. patent application Ser. No. 11/223,669,issued as U.S. Pat. No. 7,445,669, entitled “Settable CompositionsComprising Cement Kiln Dust and Additive(s),” filed Sep. 9, 2005, theentire disclosures of which are incorporated herein by reference.

BACKGROUND

The present invention relates to cementing operations and, moreparticularly, in certain embodiments, to methods and compositions thatcomprise cement kiln dust (“CKD”) and rice husk ash.

In cementing methods, such as well construction and remedial cementing,settable compositions are commonly utilized. As used herein, the term“settable composition” refers to a composition(s) that hydraulicallysets or otherwise develops compressive strength. Settable compositionsmay be used in primary cementing operations whereby pipe strings, suchas casing and liners, are cemented in well bores. In performing primarycementing, a settable composition may be pumped into an annulus betweena subterranean formation and the pipe string disposed in thesubterranean formation. The settable composition should set in theannulus, thereby forming an annular sheath of hardened cement (e.g., acement sheath) that should support and position the pipe string in thewell bore and bond the exterior surface of the pipe string to the wallsof the well bore. Settable compositions also may be used in remedialcementing methods, such as the placement of cement plugs, and in squeezecementing for sealing voids in a pipe string, cement sheath, gravelpack, formation, and the like.

Settable compositions used heretofore commonly comprise Portland cement.Portland cement generally is a major component of the cost for thesettable compositions. To reduce the cost of such settable compositions,other components may be included in the settable composition in additionto, or in place of, the Portland cement. Such components may include flyash, slag cement, shale, metakaolin, micro-fine cement, and the like.“Fly ash,” as that term is used herein, refers to the residue from thecombustion of powdered or ground coal, wherein the fly ash carried bythe flue gases may be recovered, for example, by electrostaticprecipitation. “Slag,” as that term is used herein, refers to agranulated, blast furnace by-product formed in the production of castiron and generally comprises the oxidized impurities found in iron ore.Slag cement generally comprises slag and a base, for example, such assodium hydroxide, sodium bicarbonate, sodium carbonate, or lime, toproduce a settable composition that, when combined with water, may setto form a hardened mass.

SUMMARY

The present invention relates to cementing operations and, moreparticularly, in certain embodiments, to methods and compositions thatcomprise CKD and rice husk ash.

An embodiment provides a method of cementing comprising: placing asettable composition into a subterranean formation, the settablecomposition comprising cement kiln dust, rice husk ash, and water; andallowing the settable composition to set.

Another embodiment provides a method of cementing comprising: placing asettable composition into a subterranean formation, the settablecomposition comprising cement kiln dust, rice husk ash, Portland cement,and water; and allowing the settable composition to set.

Another embodiment provides a method of cementing comprising: placing asettable composition into a subterranean formation, the settablecomposition comprising: cement kiln dust, rice husk ash, and water,wherein the cement kiln dust is present in an amount in a range of fromabout 50% to about 80% by weight of the cement kiln dust and the ricehusk ash, wherein the rice husk ash is present in an amount in a rangeof from about 20% to about 50% by weight of the cement kiln dust and therice husk ash, wherein the water is present in an amount in a range offrom about 40% to about 200% by weight of the cement kiln dust and therice husk ash, wherein the settable composition is essentially free ofPortland cement; and allowing the settable composition to set.

Another embodiment provides a settable composition comprising: cementkiln dust; rice husk ash; and water.

The features and advantages of the present invention will be readilyapparent to those skilled in the art. While numerous changes may be madeby those skilled in the art, such changes are within the spirit of theinvention.

DETAILED DESCRIPTION

The present invention relates to cementing operations and, moreparticularly, in certain embodiments, to methods and compositions thatcomprise CKD and rice husk ash. There may be several potentialadvantages to the methods and compositions of the present invention,only some of which may be alluded to herein. One of the many potentialadvantages of embodiments of the present invention is that inclusion ofrice husk ash in settable compositions comprising CKD may improve themechanical properties of the CKD-containing settable compositions. Byway of example, inclusion of rice husk ash may provide increasedcompressive strength for settable compositions comprising CKD. Anotherpotential advantage of embodiments of the present invention is that theCKD and/or rice husk ash may be used to reduce the cost of the settablecompositions. For example, use of waste CKD and/or rice husk ash toreplace a higher cost component, such as Portland cement, should resultin a more economical settable composition.

Embodiments of the settable compositions of the present invention maycomprise CKD, rice husk ash, and water. Other optional additives mayalso be included in embodiments of the settable compositions as desired,including, but not limited to, unexpanded perlite, pumicite, fly ash,slag cement, metakaolin, shale, zeolite, combinations thereof, and thelike. Embodiments of the settable compositions may also be foamed and/orextended as desired by those of ordinary skill in the art. The settablecompositions of the present invention should have a density suitable fora particular application as desired by those of ordinary skill in theart, with the benefit of this disclosure. In some embodiments, thesettable compositions may have a density in the range of from about 8pounds per gallon (“ppg”) to about 16 ppg. In other embodiments, thesettable compositions may be foamed to a density in the range of fromabout 8 ppg to about 13 ppg.

Embodiments of the settable compositions generally may comprise CKD. Asused herein, the term “CKD” refers to a partially calcined kiln feedwhich is removed from the gas stream and collected, for example, in adust collector during the manufacture of cement. Usually, largequantities of CKD are collected in the production of cement that arecommonly disposed of as waste. Disposal of the waste CKD can addundesirable costs to the manufacture of the cement, as well as theenvironmental concerns associated with its disposal. The chemicalanalysis of CKD from various cement manufactures varies depending on anumber of factors, including the particular kiln feed, the efficienciesof the cement production operation, and the associated dust collectionsystems. CKD generally may comprise a variety of oxides, such as SiO₂,Al₂O₃, Fe₂O₃, CaO, MgO, SO₃, Na₂O, and K₂O.

The CKD generally may exhibit cementitious properties, in that it mayset and harden in the presence of water. In accordance with embodimentsof the present invention, the CKD may be used, among other things, toreplace higher cost cementitious components, such as Portland cement,resulting in more economical settable compositions. In addition,substitution of the CKD for the Portland cement can result in a settablecomposition with a reduced carbon footprint.

The CKD may be included in the settable compositions in an amountsufficient to provide the desired compressive strength, density, costreduction, and/or reduced carbon footprint. In some embodiments, the CKDmay be present in the settable compositions of the present invention inan amount in the range of from about 0.1% to about 99% by weight ofcementitious components. Cementitious components include thosecomponents or combinations of components of the settable compositionsthat hydraulically set, or otherwise harden, to develop compressivestrength, including, for example, CKD, rice husk ash, unexpandedperlite, fly ash, pumicite, slag, lime, shale, and the like. The CKD maybe present, in certain embodiments, in an amount ranging between any ofand/or including any of about 0.1%, about 1%, about 5%, about 10%, about15%, about 20%, about 25%, about 30%, about 35%, about 40%, about 45%,about 50%, about 55%, about 60%, about 65%, about 70%, about 75%, about80%, about 90%, about 95%, or about 99%. In one embodiment, the CKD maybe present in the settable compositions in an amount in the range offrom about 5% to about 95% by weight of cementitious components. Inanother embodiment, the CKD may be present in an amount in the range offrom about 50% to about 95% by weight of cementitious components. In yetanother embodiment, the CKD may be present in an amount in the range offrom about 50% to about 80% by weight of cementitious components. One ofordinary skill in the art, with the benefit of this disclosure, willrecognize the appropriate amount of CKD to include for a chosenapplication.

Embodiments of the settable compositions generally may comprise ricehusk ash. As used herein, the term “rice husk” refers to the hardprotective coverings of grains of rice that are separated from the riceduring production. Rice husks are also commonly referred to as ricehulls or rice shells. Large quantities of rice husks are typicallygenerated during the production of rice that are usually disposed of aswaste. However, disposal of the rice husks in landfills can beproblematic as space in landfills may be limited. The rice huskstypically contains a substantially amount of silica and when burnedyield an ash, referred to herein as “rice husk ash,” which is rich inamorphous silica. In some embodiment, the ash obtained from combustionof the rice husks may be further processed by dry grinding the ash to apowder form.

Addition of the rice husk ash to settable compositions comprising CKDhas been shown to provide increases in compressive strength. Inaccordance with present embodiments, the rice husk ash may be includedin CKD-containing settable compositions to increase the compressivestrength thereof. By way of example, inclusion of the rice husk ash in asettable compositions comprising CKD may increase the compressivestrength in an amount greater than or equal to about 10% in oneembodiment, greater than or equal to about 25% in another embodiment,greater than or equal to about 50% in another embodiment, and greaterthan or equal to about 75% in yet another embodiment, as compared to thesame settable composition that does not contain the latex strengthenhancer. As used herein, “compressive strength” is measured at aspecified time after the composition has been mixed and the compositionis maintained under specified temperature and pressure conditions. Forexample, compressive strength can be measured at a time in the range ofabout 24 to about 48 hours after the composition is mixed and thecomposition is maintained at a temperature of 160° F. and atmosphericpressure. Compressive strength can be measured by either a destructivemethod or non-destructive method. The destructive method physicallytests the strength of settable composition samples at various points intime by crushing the samples in a compression-testing machine. Thecompressive strength is calculated from the failure load divided by thecross-sectional area resisting the load and is reported in units ofpound-force per square inch (psi). Non-destructive methods typically mayemploy an Ultrasonic Cement Analyzer (“UCA”), available from FannInstrument Company, Houston, Tex.

In some embodiments, the rice husk ash may be present in the settablecompositions of the present invention in an amount in the range of fromabout 0.1% to about 99% by weight of cementitious components. The ricehusk ash may be present, in certain embodiments, in an amount rangingbetween any of and/or including any of about 0.1%, about 1%, about 5%,about 10%, about 15%, about 20%, about 25%, about 30%, about 35%, about40%, about 45%, about 50%, about 55%, about 60%, about 65%, about 70%,about 75%, about 80%, about 90%, about 95%, or about 99%. In oneembodiment, the rice husk ash may be present in the settablecompositions in an amount in the range of from about 5% to about 95% byweight of cementitious components. In another embodiment, the rice huskash may be present in an amount in the range of from about 5% to about50% by weight of cementitious components. In yet another embodiment, therice husk ash may be present in an amount in the range of from about 20%to about 50% by weight of cementitious components. One of ordinary skillin the art, with the benefit of this disclosure, will recognize theappropriate amount of rice husk ash to include for a chosen application.

The water that may be used in embodiments of the settable compositionsincludes, for example, freshwater, saltwater (e.g., water containing oneor more salts dissolved therein), brine (e.g., saturated saltwaterproduced from subterranean formations), seawater, or combinationsthereof. Generally, the water may be from any source, provided that thewater does not contain an excess of compounds that may undesirablyaffect other components in the settable composition. In someembodiments, the water may be included in an amount sufficient to form apumpable slurry. In some embodiments, the water may be included in thesettable compositions of the present invention in an amount in the rangeof about 40% to about 200% by weight of cementitious components. In someembodiments, the water may be included in an amount in the range ofabout 40% to about 150% by weight of cementitious components. One ofordinary skill in the art, with the benefit of this disclosure, willrecognize the appropriate amount of water to include for a chosenapplication.

In some embodiments, the settable compositions may further comprise ahydraulic cement. A variety of hydraulic cements may be utilized inaccordance with the present invention, including, but not limited to,those comprising calcium, aluminum, silicon, oxygen, iron, and/orsulfur, which set and harden by reaction with water. Suitable hydrauliccements include, but are not limited to, Portland cements, pozzolanacements, gypsum cements, high alumina content cements, silica cements,and any combination thereof. In certain embodiments, the hydrauliccement may comprise a Portland cement. In some embodiments, the Portlandcements that are suited for use in the present invention are classifiedas Classes A, C, H, and G cements according to American PetroleumInstitute, API Specification for Materials and Testing for Well Cements,API Specification 10, Fifth Ed., Jul. 1, 1990. In addition, in someembodiments, cements suitable for use in the present invention mayinclude cements classified as ASTM Type I, II, or III.

It should be understood that use of hydraulic cement in embodiments ofthe settable compositions in addition to the CKD and/or rice husk ashcan be reduced or even eliminated to provide, for example, the desiredcost savings and/or reduced carbon footprint. Accordingly, embodimentsof the settable compositions of the present invention may comprisehydraulic cement in an amount of 0% to about 75%. For example, thehydraulic cement may be present, in certain embodiments, in an amountranging between any of and/or including any of about 1%, about 5%, about10%, about 15%, about 20%, about 24%, about 25%, about 30%, about 35%,about 40%, about 50%, about 55%, about 60%, about 65%, about 70%, orabout 75%. In an embodiment, the hydraulic cement may be present in anamount in the range of from about 0% to about 20%. In anotherembodiment, the hydraulic cement may be present in an amount in therange of from about 0% to about 10%. In yet another embodiment, thesettable compositions may be essentially free of hydraulic cement. Asused herein, the term “essentially free” means that hydraulic cement isnot present or, to the extent, that trace amounts of hydraulic cementmay be present, is present in an amount less than about 1% by weight ofcementitious components. In certain embodiments, the settablecomposition may contain hydraulic cement in an amount less than about0.1% by weight of cementitious components and, alternatively, less thanabout 0.01% by weight of cementitious components. By way of example, thesettable composition, in certain embodiments, may be free of hydrauliccement, in that the settable composition contains no hydraulic cement.

Embodiments of the settable compositions further may comprise a setretarding additive. As used herein, the term “set retarding additive”refers to an additive that retards the setting of the settablecompositions of the present invention. Examples of suitable setretarding additives include, but are not limited to, ammonium, alkalimetals, alkaline earth metals, metal salts of sulfoalkylated lignins,organic acids (e.g., hydroxycarboxy acids), copolymers that compriseacrylic acid or maleic acid, and combinations thereof. One example of asuitable sulfoalkylated lignin comprises a sulfomethylated lignin.Suitable set retarding additives are disclosed in more detail in U.S.Pat. No. Re. 31,190, the entire disclosure of which is incorporatedherein by reference. Suitable set retarding additives are commerciallyavailable from Halliburton Energy Services, Inc. under the trademarksHR® 4, HR® 5, HR® 7, HR® 12, HR®15, HR®25, HR 601, SCR™ 100, and SCR™500 retarders. Generally, where used, the set retarding additive may beincluded in the settable compositions of the present invention in anamount sufficient to provide the desired set retardation. In someembodiments, the set retarding additive may be present in the settablecompositions of the present invention an amount in the range of about0.1% to about 5% by weight of cementitious components. One of ordinaryskill in the art, with the benefit of this disclosure, will recognizethe appropriate amount of the set retarding additive to include for achosen application.

Optionally, other additional additives may be added to the settablecompositions of the present invention as deemed appropriate by oneskilled in the art, with the benefit of this disclosure. Examples ofsuch additives include, but are not limited to, strength-retrogressionadditives, set accelerators, weighting agents, lightweight additives,gas-generating additives, mechanical property enhancing additives,lost-circulation materials, filtration-control additives, dispersants,fluid-loss-control additives, defoaming agents, foaming agents,oil-swellable particles, water-swellable particles, thixotropicadditives, and combinations thereof. Specific examples of these, andother, additives include unexpanded perlite, pumicite, fly ash, slagcement, metakaolin, shale, zeolite, crystalline silica, amorphoussilica, fumed silica, salts, fibers, hydratable clays, microspheres,elastomers, elastomeric particles, resins, latex, combinations thereof,and the like. A person having ordinary skill in the art, with thebenefit of this disclosure, will readily be able to determine the typeand amount of additive useful for a particular application and desiredresult.

In some embodiments, the CKD and the rice husk ash may be combined toform a cementitious component. In addition to the CKD and rice husk ash,additional components may also be included in the cementitious componentas filler or for other purposes as will be apparent to one of ordinaryskill in the art with the benefit of this disclosure. For example, othercomponents that may set and harden in the presence of water can also beincluded in the cementitious component. In some embodiments, thecementitious component further may comprise unexpanded perlite,pumicite, fly ash, slag cement, metakaolin, shale, zeolite, orcombinations thereof. In some embodiments, the cementitious componentmay be placed in a bag or other suitable container for storage and/ordelivery to a well site. In an embodiment, the cementitious componentmay then be combined with water to create a settable composition.

In some embodiments, the components of the settable compositions may becombined in any order as will be appreciated by those of ordinary skillin the art. In one embodiment, the CKD and rice husk ash may be combinedwith water to create a settable composition. As will be appreciated, oneor more additional components as described above, for example, may alsobe included in the settable composition. The components of the settablecomposition may be combined using any mixing device compatible with thecomposition as known to one of ordinary skill in the art, for example abulk mixer.

As will be appreciated by those of ordinary skill in the art,embodiments of the settable compositions may be used in a variety ofsubterranean applications, including primary and remedial cementing.Embodiments of the settable compositions may be introduced into asubterranean formation and allowed to set therein. For example, thesettable composition may be placed into a space between a subterraneanformation and a conduit located in the subterranean formation. As usedherein, introducing the settable composition into a subterraneanformation includes introduction into any portion of the subterraneanformation, including, without limitation, into a well bore drilled intothe subterranean formation, into a near well bore region surrounding thewell bore, or into both.

In primary cementing embodiments, for example, a settable compositionmay be introduced into a space outside a conduit (e.g., pipe strings,liners) located in the subterranean formation. The conduit may belocated in a well bore drilled into the subterranean formation. Thesettable composition may be allowed to set to form an annular sheath ofhardened cement in the space outside conduit. Among other things, theset settable composition may Irwin a barrier, preventing the migrationof fluids in the well bore. The set settable composition also may, forexample, support the conduit in the well bore.

In remedial cementing embodiments, a settable composition may be used,for example, in squeeze-cementing operations or in the placement ofcement plugs. By way of example, the settable composition may be placedin a well bore to plug a void or crack in the formation, in a gravelpack, in the conduit, in the cement sheath, and/or a microannulusbetween the cement sheath and the conduit.

To facilitate a better understanding of the present invention, thefollowing example of certain aspects of some embodiments is given. In noway should the following example be read to limit, or define, the scopeof the invention.

EXAMPLE

A series of sample settable compositions were prepared and tested toanalyze the force resistance properties of settable compositions thatcomprise CKD and rice husk ash. The sample compositions were allowed tocure in a water bath at 160° F. for 24 hours at ambient pressure.Immediately after removal from the water bath, crush strengths(destructive compressive strengths) were determined using a Tinius Olsentester. The results of the crush strength tests are set forth in thetable below.

Ten different tests were conducted, designated Test Nos. 1-10, using theindicated amounts of water, CKD, rice husk ash, hydrated lime, andcement dispersant. The amounts of these components are indicated in thetable below with percent by weight (“% by wt”) indicating the percent ofthe component by weight of the cement and rice husk ash. The amount ofrice husk ash was varied in an amount ranging from 0% to 50% by weight.Tests 1 and 5 were comparative tests that did not include any rice huskash. The dispersant used was CFR-3™ cement friction reducer, fromHalliburton Energy Services, Inc., Duncan, Okla. The CKD used wassupplied by Holcem (US) Inc., from Ada, Okla. The rice husk ash used wassupplied by Riceland Foods, Inc., Stuttgart, Ark., and had particlesranging from about 1 micron to about 10 microns.

TABLE 1 Crush Strength Tests 24-Hr Water Rice Hydrate Dis- Crush Test (%by CKD (% Husk Ash Lime (% persant Strength No. wt) by wt) (% by wt) bywt) (% by wt) (psi) 1 48.75 100 — — 0.75 1437 2 48.9 95  5 — 0.75 1542 350.64 95  5 5 0.75 1400 4 49.06 90 10 — 0.75 1556 5 89.72 100 — — — 2756 90.5 80 20 — — 417 7 90.69 75 25 — — 483 8 90.89 70 30 — — 532 9 91.2860 40 — — 446 10 91.67 50 50 — 0.75 479

This example thus indicates that inclusion of the rice husk ash providesstrength enhancement to CKD-containing compositions. Indeed, increasesin compressive strength of 50% or more were obtained for Tests No. 6-10having a density of 12.5 ppg and containing rice husk ash in an amountranging from 20% to 50% by weight, as compared to Test No. 5 that didnot contain any rice husk ash.

It should be understood that the compositions and methods are describedin terms of “comprising,” “containing,” or “including” variouscomponents or steps, the compositions and methods can also “consistessentially of” or “consist of” the various components and steps.

For the sake of brevity, only certain ranges are explicitly disclosedherein. However, ranges from any lower limit may be combined with anyupper limit to recite a range not explicitly recited, as well as, rangesfrom any lower limit may be combined with any other lower limit torecite a range not explicitly recited, in the same way, ranges from anyupper limit may be combined with any other upper limit to recite a rangenot explicitly recited. Additionally, whenever a numerical range with alower limit and an upper limit is disclosed, any number and any includedrange falling within the range is specifically disclosed. In particular,every range of values (of the form, “from about a to about b,” or,equivalently, “from approximately a to b,” or, equivalently, “fromapproximately a-b”) disclosed herein is to be understood to set forthevery number and range encompassed within the broader range of valueseven if not explicitly recite. Thus, every point or individual value mayserve as its own lower or upper limit combined with any other point orindividual value or any other lower or upper limit, to recite a rangenot explicitly recited.

Therefore, the present invention is well adapted to attain the ends andadvantages mentioned as well as those that are inherent therein. Theparticular embodiments disclosed above are illustrative only, as thepresent invention may be modified and practiced in different butequivalent manners apparent to those skilled in the art having thebenefit of the teachings herein. Although individual embodiments arediscussed, the invention covers all combinations of all thoseembodiments. Furthermore, no limitations are intended to the details ofconstruction or design herein shown, other than as described in theclaims below. Also, the terms in the claims have their plain, ordinarymeaning unless otherwise explicitly and clearly defined by the patentee.It is therefore evident that the particular illustrative embodimentsdisclosed above may be altered or modified and all such variations areconsidered within the scope and spirit of the present invention.

1. A settable composition comprising: cement kiln dust; rice husk ash;and water.
 2. The composition of claim 1 wherein the settablecomposition has a density in a range of from about 8 pounds per gallonto about 16 pounds per gallon, and wherein the water is present in anamount in a range of from about 40% to about 200% by weight ofcementitious components.
 3. The composition of claim 1 wherein thecement kiln dust is present in an amount in a range of from about 50% toabout 95% by weight of cementitious components.
 4. The composition ofclaim 1 wherein the cement kiln dust is present in an amount in a rangeof from about 70% to about 95% by weight of cementitious components. 5.The composition of claim 1 wherein the cement kiln dust is present in anamount in a range of from about 90% to about 95% by weight ofcementitious components.
 6. The composition of claim 1 wherein the ricehusk ash is present in an amount in a range of from about 5% to about50% by weight of cementitious components.
 7. The composition of claim 1wherein the rice husk ash is included in the settable composition in anamount sufficient to increase the 24-hour destructive compressivestrength of the settable composition at 160° F. and atmospheric pressurein an amount equal to or greater than about 10%.
 8. The composition ofclaim 1 wherein the rice husk ash is included in the settablecomposition in an amount sufficient to increase the 24-hour destructivecompressive strength of the settable composition at 160° F. andatmospheric pressure in an amount equal to or greater than about 75%. 9.The composition of claim 1 wherein the settable composition isessentially free of hydraulic cement in addition to the cement kilndust.
 10. The composition of claim 1 wherein the settable compositionfurther comprises at least one additive selected from the groupconsisting of unexpanded perlite, pumicite, lime, fly ash, slag cement,metakaolin, shale, zeolite, crystalline silica, amorphous silica, fumedsilica, salt, fiber, hydratable clay, microsphere, elastomer,elastomeric particle, resin, latex, and any combination thereof.
 11. Thecomposition of claim 1 wherein the settable composition furthercomprises at least one additive selected from the group consisting of aset-retarding additive, strength-retrogression additive, a setaccelerator, a weighting agent, a lightweight additive, a gas-generatingadditive, a mechanical property enhancing additive, a lost-circulationmaterial, a filtration-control additive, a dispersant, afluid-loss-control additive, a defoaming agent, a foaming agent, anoil-swellable particle, a water-swellable particle, a thixotropicadditive, and any combination thereof.
 12. A settable compositioncomprising: a partially calcined kiln feed removed from a gas stream,wherein the partially calcined kiln feed comprises SiO₂, Al₂O₃, Fe₂O₃,CaO, MgO, SO₃, Na₂O, and K₂O; rice husk ash; and water.
 13. Thecomposition of claim 12 wherein the partially calcined kiln feed ispresent in an amount in a range of from about 50% to about 95% by weightof cementitious components, and wherein the rice husk ash is present inan amount in a range of from about 5% to about 50% by weight ofcementitious components.
 14. The composition of claim 12 wherein thepartially calcined kiln feed is present in an amount in a range of fromabout 70% to about 95% by weight of cementitious components.
 15. Thecomposition of claim 12 wherein the partially calcined kiln feed ispresent in an amount in a range of from about 90% to about 95% by weightof cementitious components.
 16. The composition of claim 12 wherein thepartially calcined kiln feed is from the manufacture of cement.
 17. Thecomposition of claim 12 wherein the rice husk ash is included in thesettable composition in an amount sufficient to increase the 24-hourdestructive compressive strength of the settable composition at 160° F.and atmospheric pressure in an amount equal to or greater than about10%.
 18. The composition of claim 12 wherein the rice husk ash isincluded in the settable composition in an amount sufficient to increasethe 24-hour destructive compressive strength of the settable compositionat 160° F. and atmospheric pressure in an amount equal to or greaterthan about 75%.
 19. The composition of claim 12 wherein the settablecomposition is essentially free of hydraulic cement in addition to thecement kiln dust.
 20. The composition of claim 12 wherein the settablecomposition further comprises at least one additive selected from thegroup consisting of unexpanded perlite, pumicite, lime, fly ash, slagcement, metakaolin, shale, zeolite, crystalline silica, amorphoussilica, fumed silica, salt, fiber, hydratable clay, microsphere,elastomer, elastomeric particle, resin, latex, and any combinationthereof.
 21. The composition of claim 12 wherein the settablecomposition further comprises at least one additive selected from thegroup consisting of a set-retarding additive, strength-retrogressionadditive, a set accelerator, a weighting agent, a lightweight additive,a gas-generating additive, a mechanical property enhancing additive, alost-circulation material, a filtration-control additive, a dispersant,a fluid-loss-control additive, a defoaming agent, a foaming agent, anoil-swellable particle, a water-swellable particle, a thixotropicadditive, and any combination thereof.
 22. A settable compositioncomprising: cement kiln dust in an amount in a range of from about 50%to about 95% by weight of cementitious components; rice husk ash in anamount sufficient to increase the 24-hour destructive compressivestrength of the settable composition at 160° F. and atmospheric pressurein an amount equal to or greater than about 10%; and water in an amountin a range of from about 40% to about 200% by weight of cementitiouscomponents, wherein the settable composition has a density in a range offrom about 8 pounds per gallon to about 16 pounds per gallon.
 23. Thecomposition of claim 22 wherein the cement kiln dust is present in anamount in a range of from about 70% to about 95% by weight ofcementitious components.
 24. The composition of claim 22 wherein thesettable composition further comprises at least one additive selectedfrom the group consisting of unexpanded perlite, pumicite, lime, flyash, slag cement, metakaolin, shale, zeolite, crystalline silica,amorphous silica, fumed silica, salt, fiber, hydratable clay,microsphere, elastomer, elastomeric particle, resin, latex, and anycombination thereof.
 25. The composition of claim 22 wherein thesettable composition further comprises at least one additive selectedfrom the group consisting of a set-retarding additive,strength-retrogression additive, a set accelerator, a weighting agent, alightweight additive, a gas-generating additive, a mechanical propertyenhancing additive, a lost-circulation material, a filtration-controladditive, a dispersant, a fluid-loss-control additive, a defoamingagent, a foaming agent, an oil-swellable particle, a water-swellableparticle, a thixotropic additive, and any combination thereof.